Use the stats component to keep an eye on various metrics (FPS,
vertex and face count, geometry and material count, draw calls, number of
entities). We want to maximize FPS and minimize everything else.

Limit draw calls as much as possible. Each geometry, object, model without
optimization is generally a draw call. Rule of thumb, try to keep under 300
maximum. Merge together all static meshes if possible. You
can use geometry-merger and then make use a three.js
material with vertex colors enabled. three.js geometries keep data such as
color, uvs per vertex that can be used to maintain and manipulate geometries
post-merge.

If using models, look to bake your lights into textures rather than relying
on real-time lighting and shadows.

Generally, the fewer number of entities and lights in the scene, the better.

Make sure your textures’ resolutions are sized to powers of two (e.g.,
256x256, 512x1024) in order to avoid the renderer having to resize the
texture during runtime.

Limit the number of faces and vertices on models.

Some further techniques include geometry instancing, geometry
merging, level of detail (LOD).

When using raycasters or colliders, select which entities are to be raycasted
against rather than raycasting against every object in the scene.

When adding continuously running behaviors, use A-Frame component tick
handlers to hook into the global render loop. Use utilities such as
AFRAME.utils.throttleTick to limit the number of times the tick handler
is run if appropriate.

Use the background component instead of a-sky to define a
solid color as the scene background. This prevents the creation of
unnecessary geometry.

Update position, rotation, scale, and visible using at the three.js
level (el.object3D.position, el.object3D.rotation, el.object3D.scale,
el.object3D.visible) to avoid overhead on .setAttribute.

When using the animation component, [animate values
directly][animationdirect] which will skip .setAttribute and animate JS
values directly. For example, instead of material.opacity, animate
components.material.material.opacity.

GPU Texture Preloading

Until non-blocking texture uploads to the GPU are available, try to draw all
materials and textures up front. When materials and textures are drawn for the
first time, the browser will hang and block while uploading to the GPU. We can
manually preload textures by calling:

We will try to come with a convenient API in A-Frame to do this automatically.

For example, this is apparent in the 360° image gallery. If we look at
the browser performance tools, there will be frame drops when switching to a
new image for the first time, but smooth transitions when switching back to
images for the second time.

Reuse materials and textures as much as possible, aiming for a small number
of unique materials. Texture atlases provide one efficient way to reuse
materials while giving the impression of more variety. Simpler three.js
materials such as MeshLambertMaterial or MeshBasicMaterial perform better
and are often sufficient for low-poly scenes.

In particular, pre-baked lighting on an unlit (Basic) material can
significantly improve performance. A-Frame’s default PBR-based (Standard)
material is more physically realistic, but also more expensive and often
unnecessary in simple scenes.

Minimizing Garbage Collection in JavaScript

Avoid creating garbage and instantiating new JavaScript objects, arrays,
strings, and functions as much as possible. In the 2D web, it is not as big of
a deal to create a lot of JavaScript objects since there is a lot of idle time
for the garbage collector to run. For VR, garbage collection may cause dropped
frames as it pauses to clean up memory. To avoid this, we try to minimize
allocation of memory and hold onto objects to prevent them from getting garbage
collected.

Learn more about detecting allocations and garbage collection in
Firefox and Chrome performance tools.

Try to avoid patterns such as Object.keys(obj).forEach(function () { });,
which create new arrays, functions, and callbacks versus using for (key in
obj). Or for array iteration, avoid .forEach and use a simple for loop
instead. Avoid unnecessary copying of objects, using methods like
utils.extend(target, source) instead of utils.clone or .slice.

tick Handlers

In component tick handlers, be frugal on creating new objects. Try to reuse
objects. A pattern to create private reusable auxiliary variables is with a
closure. Below we create a helper vector and quaternion and reuse them between
frames, rather than creating new ones on each frame. Be careful that these
variables do not hold state because they will be shared between all instances
of the component. Doing this will reduce memory usage and garbage collection:

Also if we continuously modify a component in the tick, make sure we pass the
same object for updating properties. A-Frame will keep track of the latest
passed object and disable type checking on subsequent calls for an extra speed
boost. Here is an example of a recommended tick function that modifies the
rotation on every tick:

Again be careful what you do in tick functions, treat them as critical
performance code because they will be run 90 times per second.

VR Design

Designing for VR is different than designing for flat experiences. As a new
medium, there are new sets of best practices to follow, especially to maintain
user comfort and presence. This has been thoroughly written about so we defer
to these guides. Note that VR interaction design is fairly new, and nothing is
absolute:

The common golden rule is to never unexpectedly take control of the camera
away from users.

Units (such as for position) should be considered meters. This is because the
WebVR API returns pose in meters which is fed into most camera controls. By
considering units as meters, we achieve expected scale.

Make use of hands and controllers. For best experience, target your application
to a specific form factor versus watering it down for all platforms at once.